libslic3r: include tbb/spin_mutex to fix compilation error (#7505)

PrintObject.cpp references tbb::spin_mutex, thus it needs to include
tbb/spin_mutex. Otherwise compilation fails with:

error: ‘spin_mutex’ is not a member of ‘tbb’

Supersedes #7057

flatpak/io.github.softfever.OrcaSlicer.yml

@@ -304,8 +304,6 @@ modules:
       # OrcaSlicer Source Archive
       - type: dir 
         path: ../
-      - type: patch
-        path: patches/libslic3r_missing_include.patch 
 
       # AppData metainfo for Gnome Software & Co.
       - type: file

flatpak/patches/libslic3r_missing_include.patch

@@ -1,12 +0,0 @@
-diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
-index 528a72e70..1530fe655 100644
---- a/src/libslic3r/PrintObject.cpp
-+++ b/src/libslic3r/PrintObject.cpp
-@@ -31,6 +31,7 @@
- #include <boost/log/trivial.hpp>
- 
- #include <tbb/parallel_for.h>
-+#include <tbb/spin_mutex.h>
- 
- #include <Shiny/Shiny.h>
- 

src/libslic3r/PrintObject.cpp

@@ -31,6 +31,7 @@
 #include <boost/log/trivial.hpp>
 
 #include <tbb/parallel_for.h>
+#include <tbb/spin_mutex.h>
 
 #include <Shiny/Shiny.h>